是否存在用于定义发动机负载的理论方程式？
这不是理论上的，而是真实的。根据SAE International SAE J1979 / ISO 15031-5（日期：2014-08-11），计算出的发动机负载通过以下公式计算：
LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) *
(BARO/29.92) * SQRT(298/(AAT+273))]
Where:
- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO,
- SQRT = square root
- WOT = wide open throttle
- AAT = Ambient Air Temperature (in °C)
Characteristics of LOAD_PCT are:
- Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally
aspirated and boosted engines.
- Indicates percent of peak available torque.
- Linearly correlated with engine vacuum
- Often used to schedule power enrichment.
- Compression ignition engines (diesels) shall support this PID using fuel
flow in place of airflow for the above calculations.
这部分的第二部分（特性）为您提供了许多您正在寻找的信息。由公式给出的百分比表示峰值可用转矩的百分比。
ECU会查看哪些参数来检测和确定发动机负载？我认为没有一个能够告诉您发动机负载的全能传感器。这里可能合并了几个信号。
它没有一个传感器可以解决这个问题。对于汽油（或火花点火）发动机，它利用进气传感器（IAT），歧管绝对压力（MAP）传感器，节气门位置传感器（TPS）和发动机冷却液温度（ECT）传感器进行计算并确定是否引擎已准备就绪，可以进行计算了。百分比变量可以使用PID $ 04从ECU读取。根据该标准，需要同时使用压缩点火（柴油）和火花点火（汽油）系统。
某些ECU似乎在相对和绝对发动机负载之间进行了区分。两者有什么区别？
您已经看到了上面的公式，用于计算发动机负荷。以下是发动机绝对负载的计算：
LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) *
cylinder displacement in liters]
Derivation:
- air mass (g / intake stroke) = [total engine air mass (g/sec)] /
[rpm (revs/min)* (1 min / 60 sec) * (1/2 # of cylinders (strokes / rev)]
- LOAD_ABS = [air mass (g)/intake stroke] / [maximum air mass (g)/intake
stroke at WOT@STP at 100% volumetric efficiency] * 100%.
Where:
- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg (101.3 kPa)
BARO
- WOT = wide open throttle
The quantity (maximum air mass (g)/intake stroke at WOT@STP at 100%
volumetric efficiency) is a constant for a given cylinder swept volume.
The constant is 1.184 (g/liter 3) * cylinder displacement (liter 3/intake
stroke) based on air density at STP.
Characteristics of LOAD_ABS are:
- Ranges from 0 to approximately 0.95 for naturally aspirated engines,
0 – 4 for boosted engines
- Linearly correlated with engine indicated and brake torque,
- Often used to schedule spark and EGR rates,
- Peak value of LOAD_ABS correlates with volumetric efficiency at WOT.
- Indicates the pumping efficiency of the engine for diagnostic purposes.
您可能会看到，该方程式依赖于空气流动以及发动机排量。正如其在人体中所陈述的那样，这与WOT时的容积效率（进气冲程中气缸充满空气的程度）有关。可从ECU上通过PID $ 43读取此变量。仅火花点火系统的标准要求。